The present invention relates to a variable compression system for internal combustion engines, and more particularly to the system wherein compression ratio of the engine can be varied during its periods of operation by means of hydraulic pressure.
In an internal combustion engine, intended enhancement of the power output and reduction of the specific fuel consumption may be achieved by increasing the compression ratio. However, the increase in the compression ratio disadvantageously invites occurrence of knocking in the heavy load zone and/or the low speed zone of the engine. Thus, in the conventional internal combustion engine whose compression ratio is constant, its practicable compression ratio must be set up inevitably at such a low level as not to cause knocking in the heavy load zone and/or the low speed zone. This results in that it is impossible to output a sufficient power and reduce the specific fuel comsumption in the light load zone and/or the high speed zone.
Several attempts to vary the compression ratio of the internal combustion engine in operation have been proposed for example in U.S. Pat. Nos. 2,040,652 to Gaty, 2,970,581 to Georges and 2,163,015 to Wagner. The systems as disclosed in the U.S. Pat. Nos. 2,040,652 and 2,970,581 are designed to conduct the variation of the compression ratio by back and forth movement of a diaphragm (U.S. Pat. No. 2,404,652) or a sub-piston (U.S. Pat. No. 2,970,581) associated with a combustion chamber, in which the diaphragm (or the sub-piston) is moved toward or away from the combustion chamber by regulating the flow of pressure oil into and out of a rear chamber provided at the back (upper side) of the diaphragm (or the sub-piston) in accordance with variable loads upon the engine. According to this prior technique arrangement, however, due to an intense pressure (approximetely 50 kg/cm.sup.2 in the case of a gasoline engine) produced by explosion of the fuel-air mixture in the combustion chamber, the diaphragm (or the sub-piston) is disadvantageously forced to move axially rearwardly (upwardly) thereby to produce an excessively high pressure in the aforesaid rear chamber, which causes the pressure oil to flow back from the rear chamber into an oil pressure regulator and further into a hydraulic pump through conduits for supplying the pressure oil in accordance with the variable loads on the engine. For this reason, the regulator and the conduits should have strength enough to endure the intense pressure caused by the explosion, and also the hydraulic pump should have the pumping capacity enough to surpass the back-flow pressure of the oil, which inevitably invites a disadvantageously large dimension and heavy weight of the system. Besides, these prior art systems will not work as expected because the regulation of the compression ratio is accompanied by an intolerably large error under the intense explosion pressure.
According to the system as disclosed in the referred U.S. Pat. No. 2,163,015, the compression ratio is varied by a cam mechanism connected to a sub-piston. The cam mechanism includes a cam mounted on a cam shaft which can be driven by a hydraulic cylinder adapted to act in accordance with variable engine speeds. A piston rod is connected at its lower end to a sub-piston reciprocable up and down within a sub-cylinder, and engaged at its upper end with the cam, so that the clearance volume of a combustion chamber can be varied upon movement of the sub-piston. Also in this case, the above described back-flow of the pressure oil occurs under the intense explosion pressure. Thus, this particular system is also subjected to the same or similar disadvantages as those inherent to the system as disclosed in the above referred in U.S. Pat. Nos. 2,040,652, and 2,970,581.
In order to solve the above discussed problem derived from the undesirable back-flow of the actuating oil (pressure oil), an attempt has been made as disclosed in Japanese patent application Laid-open No. 88926/81. The arrangement proposed therein comprises a hydraulic cylinder, a plunger disposed within the hydraulic cylinder so as to be coaxial and engageable with a piston rod connected at lower end to a sub-piston for varying the compression ratio, a change-over valve provided in a pressure oil conduit connected to the hydraulic cylinder for switching over its positions from feed position to release position and vice versa, the change-over valve being so arranged that it takes its feed position in the light load zone and/or the high speed zone of the engine, for supplying the pressure oil into the hydraulic cylinder thereby to move the sub-piston toward the combustion chamber, while in the heavy load zone and/or the low speed zone of the engine, it takes its release position for releasing the pressure oil from the hydraulic cylinder into atmosphere thereby to move the sub-piston away from the combustion chamber, and a check valve provided in a passageway extending from the changeover valve to the hydraulic cylinder for oneway flow to the hydraulic cylinder, so that pressure rise in the hydraulic cylinder, due to the expansion in the combustion chamber, does not invite the undesirable back-flow of the pressure-oil into the hydraulic units located upstream of the check valve.
According to this prior art system, because the changeover valve is so arranged that, at a certain critical value of the enginge load or the engine speed, it takes the alternative of its feed position for supplying the pressure oil to the hydraulic cylinder, or its release position for releasing the pressure oil from the hydraulic cylinder, the reglation for the back and forth movement of the sub-piston, and hence, for the compression ratio, is performed in a radical manner where the compression ratio is stepped from a high ratio phase to a low ratio phase or vice versa, at a certain critical valve of the engine load or the engine speed. In other words, the compression ratio cannot be varied steplessly in propotion to values of the engine load or the engine speed. Thus, this prior art system is subjected to such particular disadvantages that not only frequent occurrences of knocking but also considerable fluctuations of the engine torques are brought about by the radical variation in the compression ratio.
Further, in this case, the following disadvantages are invited by its specific construction that the piston rod of the sub-piston is operatively engaged with the plunger of the hydraulic cylinder. The first disadvantage is that the diameter of the piston rod must be large enough to resist against such a considerable compressive force exerted thereon caused by an intense explosion pressure produced in the combustion chamber. A second disadvantage is that undesirable vibrations and/or noises are produced by collisions of the piston rod against the plunger of the hydraulic cylinder.
It is, therefore, an object of the present invention to provide an improver variable compression system for internal combustion engines, in which the above-discussed disadvantages, inherent to the conventional systems or devices, can be eliminated.
Another object of the invention is to provide an improved system for controlling the compression ratio, so arranged as to prevent the pressure oil (actuating oil) from flowing back to its pressure oil source, regardless of intense oil pressure produced at the back side of a sub-piston due to the explosion conducted in a combustion chamber.
A further object of the invention is to provide an improved system for controlling the compression ratio, which permits variation of the compression ratio at a low level of hydraulic pressure.
A still further object of the invention is to provide an improved system for controlling the compression ratio, in which variation of the compression ratio can be conducted in a smooth and stepless manner, without fluctuations in the engine torques and occurrences of knocking during variation of the compression ratio.
Yet further object of the invention is to provide an improved system for controlling the compression ratio, in which variation of the compression ratio can be performed automatically or manually by a simple and easy manner with less power, in response to variable operating conditions of the engine, such as engine speeds, engine loads, knocking, ect.
Still a further object of the invention is to provide an improved system for controlling the compression ratio, which is simple in construction, compact in size, light in weight, and operable without increase in vibration and noises.
In accordance with the present invention, there is provided a variable compression system for internal combustion engines of the type that variation of the compression ratio is conducted by hydraulic regulation of back and forth movement of a sub-piston slidably mounted within a sub-cylinder which is communicated with a combustion chamber. The system of the invention comprises: (i) an pressure oil chamber formed on a back face of the sub-piston and pressurized from a pressure source, (ii) a control valve means, such as a check valve, provided in a pressure oil feed passage for checking the pressure oil feed to the pressure oil chamber, (iii) a reciprocative member, for example a stem, which is connected at one end to the sub-piston and has a part projecting out of the sub-cylinder through a closure member mounted to the back end of the sub-cylinder, the reciprocative member having an internal oil passage which is communicated with the pressure oil chamber and also with a through hole, hereinafter referred to as "a spill port", formed in the projecting part of the reciprocative member, for releasing the pressure oil introduced from the pressure oil chamber, and (iv) a spill regulation member relatively movably mounted on the projecting part of the reciprocative member for timely opening or closing the spill port in such a manner that it closes the spill port when the sub-piston moves away from the combustion chamber and opens the same when the sub-piston moves toward the combustion chamber.
In operation of the system according to the present invention, the pressure oil supply to the pressure oil chamber is performed when the spill port is closed by the spilling regulation member and when the check valve in the pressure oil feed passage takes its open position, i.e., when a force for advancing the sub-piston, derived from a pressure of the supplied pressure oil (actuating oil), is greater than a force for retracting the sub-piston, derived from a pressure in the combustion chamber, and more particularly, at the intake stroke or the exhaust stroke, for instance. At the compression stroke or the expansion stroke, on the other hand, where the compression chamber is highly pressurized, the check valve is in its closed position and therefore, an intense pressure increase in the pressure oil chamber, caused by expansion in the combustion chamber, does not invite the back-flow of the actuating oil to such hydraulic units, for example a hydraulic pump, as located at the pressure oil source side.
In such a pressure balanced condition where the spill port is slightly opened to permit continuous release of the actuating oil introduced through the pressure oil feed passage and the pressure oil chamber, the spill regulation member is moved to close the spill port. As soon as the spill port is fully closed, the release of the actuating oil therethrough is terminated, whereby the pressure in the pressure oil chamber at the intake or exhaust stroke rises up to a level of the actuating oil supplying pressure, so that the force for advancing the sub-piston toward the combustion chamber, developed by this increased pressure in the combustion chamber, becomes greater than the force for retracting the sub-piston away from the combustion chamber, resulting in that the sub-piston advances toward the combustion chamber.
When this advancement of the sub-piston proceeds to a certain extent, the spill port is again opened to start the release of the actuating oil. As soon as the released volume of the oil thru the spill port is balanced with the supplied volume of the oil into the pressure oil chamber, the advancement of the sub-piston ends.
As will be observed, the advancement of the sub-piston toward the combustion chamber is governed by supplying the actuating oil into the combustion chamber at the intake or exhaust stroke where the pressure in the pressure oil chamber is low, whereas the retraction of the sub-piston away from the combustion chamber is governed by releasing the actuating oil from the pressure oil chamber via the spill port. Therefore, pressure of the actuating oil to be supplied into the pressure oil chamber need not surpass an intense explosion pressure produced in the combustion chamber, resulting in that the actuating oil may be utilized at a low pressure level. This means that a high capacity hydraulic pump is no longer required for actuating the sub-piston. Further, such low pressure oils, for example lubricating oils for various parts of the engine, or actuating oils for power-steering or automatic transmission, can be utilized as the actuating oil for the system according to the present invention. In the case where the lubricating oil for the engine parts is utilized as the actuating oil in question, a lubricating oil pump may serve also for the actuating oil pump.
Further, the back and forth movement of the sub-piston is governed by controlling the spill regulation member so that the spill port is properly opened or closed, and thus, the compression ratio can be varied in a stepless manner.
When an intense explosion pressure is imposed upon the sub-piston at the expansion stroke, as the check valve in the pressure oil feed passage being in its closed position, the sub-piston is forced to move slightly rearwardly, whereby the spill port is closed to cause a rapid pressure increase in the pressure oil chamber. Thus, the intense explosion pressures imparted upon the sub-piston can be backed up and, at the same time, buffered by compression of the actuating oil in the pressure oil chamber behind the sub-piston. This results in that any increase in vibration and noises is not invited, though the intense explosion pressures are intermittently impacted upon the sub-piston. Further, the spilling regulation member does not move unexpectedly under the explosion pressure, and hence, the compression ratio is maintained substantially at its desired level without fluctuations thereof. In addition, relatively small power is enough to drive the spilling regulation member.
According to the present invention, no thick stem is required since the intense explosion pressure does not act thereupon as a compressive force; no extra hydraulic cylinder is required to move the sub-piston back and forth, such as those inherently provided in the prior art systems as referred to in the forgoing, additionally to the one in which the sub-piston for varying the compression ratio of the engine is mounted; a relatively low capacity hydraulic pump, usually small in size, is sufficient to use for pressurizing the actuating oil for the sub-piston because the oil can be utilized at its low pressure level; and besides, this pump may be dispensed with, in such a particular case where a lubricating oil pump serves for it; all of these features of the invention cooperatively contribute to the simple and compact construction as well as reduction in weight of the system.
The present invention has an additional feature, that an easy and ready engine starting can be attained by retracting the sub-piston, upon stopping the engine, to its rearmost position (best standby position), furthest away from the combustion chamber.
A further feature or aspect of the invention is that deterioration of the pressure oil (actuating oil), caused by the blow-by gas which penetrates through the clearance between the sub-piston and the associated sub-cylinder, can be minimized by provision of the blow-by gas chamber.
A still further feature or aspect of the invention is that the variable compression system herein disclosed is readily applicable to counter-flow type engines and also to multi-cylinder engines, such as for example, two-cylinder engines, three-cylinder engines, four-cylinder engines, and the like.
Yet a further feature or aspect of the invention is that the variable compression system herein disclosed is readily applicable not only to spark-ignition type engines but also to compression-ignition type engines.
Other objects, features and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become obvious to those skilled in the art from this detailed description.